As is well known, the great majority of internal combustion vehicles currently in use burn liquid gasoline to obtain motive power. In order to burn the gasoline, the same must be atomized and mixed with air in a carburetor. The mixture of atomized gasoline and air is then fed to the cylinders, where it burns rapidly as an explosive mixture.
Because of incomplete combustion and certain impurities in gasoline, the problem of emissions for gasoline-burning automobiles has become a serious one.
One approach to reducing noxious emissions from internal combustion engines is to burn a gaseous fuel, like natural gas, instead of gasoline. With natural gas, the mixture with air can be made relatively complete, due to the fact that two gases are being mixed, rather than an atomized liquid and a gas. Also, natural gas as it comes from the well can be treated to remove unwanted components, so that the burning is extremely clean, compared to gasoline.
Other factors also weigh in favour of using natural gas rather than gasoline. One of these factors has to do with cost. At the present time, the cost of using natural gas for automotive fuel, on a dollars per mile basis, is approximately one half of that of gasoline. Secondly, particularly in Canada and the United States, the supply of natural gas is relatively abundant from domestic wells. If all North American automobiles were converted to burn natural gas, dependence on off-shore oil imports would be greatly reduced.
Yet another advantage for natural gas as a fuel for automobiles is its safety feature. Because it is a gas, and because it is lighter than air, any leakage will result in the gas rising and dissipating. By contrast, gasoline or propane would puddle and build up a hazard. Furthermore, it takes a temperature of 700.degree. C. or better to ignite natural gas, whereas gasoline ignites at a much lower temperature (450.degree. C.), as does propane. Additionally, it takes specific natural gas to air pecentages for combustion--four to fourteen. Because this is a narrower range than that for gasoline, the likelihood of combustion other than in the engine itself is reduced.
From a pollution point of view, it has been estimated that natural gas cuts pollution by about 90% compared with gasoline. As mentioned previously, this is partly due to the fact that the gasoline droplets resulting from atomization mix imperfectly with air in the carburetor and tend to separate. By contrast, natural gas, which is already in gaseous form, mixes much more thoroughly with air and cannot be separated from it. Thus, natural gas burns more completely, more efficiently and more cleanly. Furthermore, natural gas contains no lead, as do several of the gasoline blends, and produces no particulate matter when it is burned. Additionally, natural gas produces less carbon monoxide than gasoline. Natural gas produces virtually no hydrocarbons that the sun can turn into smog.
In 1982, at least 400,000 cars and trucks around the world were already using natural gas for power. Typically, the natural gas is compressed to a pressure of around 3,000 psi and stored in one or more pressure storage tanks in the vehicle. The storage tanks are standard high-pressure tanks of the kind that helium, argon and other specialty gases are stored in. In general terms, the natural gas is bled from the tanks and passes to a pressure regulator that brings the gas pressure in the tanks down to the proper pressure for the mixer. The mixer is a unit which sits above the carburetor (in the case of a system which can burn either gasoline or natural gas) or above the throttle valve leading to the intake manifold (in the case of a vehicle burning natural gas only). The mixer is adapted to mix the appropriate quantity of air with the natural gas prior to entering the intake manifold. The mixture is then burned in the cylinders in exactly the same way as the atomized gasoline and air mixture is typically burned in a standard automobile.
The above operational system is well known. The present invention concerns more the matter of filling the storage tanks. At present, vehicles equipped with a natural gas combustion system can drive into a service station equipped with the appropriate high pressure cascade tanks, and can be filled from zero pressure to maximum pressure (3,000 psi or thereabouts) in about five minutes. However, at the present time there are only a few service stations so equipped, and it would be of advantage to be able to fill the tanks from the low pressure natural gas available in the pipes that bring natural gas to homes for heating purposes. However, the natural gas in the house lines is only a few psi above atmospheric, and needs to be compressed in order to allow the storage tanks to be filled. It is already known to provide a small compressor which is operated by an electrical motor connected to the house mains. The compressor would typically be mounted in the garage, and the automobile can be charged overnight (12 to 14 hours) using this conventional compressor.
However, for automobiles which are used continuously, such as taxis, a single fill of the storage tanks may not be sufficient for a full day's use, and if the high pressure cascade fill-up stations are not available, a problem arises in connection with refuelling.